In the field of internal combustion engines, great emphasis is being placed on the production of spark ignition engines having means for maximizing combustion of hydrocarbon fuels thereby reducing to a minimum the undesirable or hazardous exhaust emissions.
The invention relates to fuel flow control systems which provide a predetermined fuel flow to the throttle body of a spark ignition engine in response to the mass of air drawn through the throttle body by the action of the engine. Thus, the fuel flow is regulated to supply the proper mass of fuel for the particular mass of air drawn into the engine, thereby providing the optimum air-fuel ratio and ideal combustion characteristics. A number of such systems have been proposed in the prior art, examples of which are: U.S. Pat. No. 3,470,858 to Mycraft; U.S. Pat. No. 3,817,225 to Priegel; and U.S. Pat. No. 3,935,851 to Wright et al. The disclosures of the abovementioned patents are herein incorporated by reference.
U.S. Pat. No. 3,935,851, in particular, discloses a fuel flow control system utilizing an electronic circuit to control fuel flow to the throttle body. The volume of air flow through the throttle body is monitored as well as the air temperature and pressure. With this information the electronic circuit can compute the true mass air flow rate. As disclosed in the patent, fuel temperature may also be sensed to accurately determine the proper volume of fuel flow which will create the optimum mass fuel-air ratio. It is further disclosed that signals representing other engine and environmental parameters may be utilized by the control circuit to modify fuel flow. Such other parameters may be the rate of change in throttle position indicating rapid engine acceleration or deceleration thus requiring a respectively richer or leaner fuel-air ratio; engine temperature since a cold engine requires a richer fuel-air mixture; measurement of actual fuel flow rate as a check against desired fuel flow rate; and exhaust gas parameters as a final check for proper combustion.
All of the systems of the above-mentioned patents provide means for monitoring engine or environmental parameters, and in response thereto control the flow of fuel to the engine by varying the speed of a fuel metering pump. One problem which has been encountered with these systems is that it is extremely difficult to produce an economical metering pump which may be controlled to provide the extremely accurate flow rates necessary for effecting a continually optimum fuel-air ratio. The main drawback in using a metering pump is that the output of the pump may be affected by changing pressure differentials across the pump working members. While the effect of this problem may be reduced by the apparatus disclosed by Meyer et al in U.S. Pat. No. 3,908,360, the accuracy of the system is still dependent on the precision and dependability of a relatively expensive metering pump.